Human neutrophil elastase and cathepsin G have been implicated in the tissue destruction associated with a number of inflammatory diseases such as chronic bronchitis, cystic fibrosis, and rheumatoid arthritis. H. L. Malech and J. I. Gallin, New Engl. J. Med., 317(11), 687 (1987). Both elastase and cathepsin G have a broad range of proteolytic activity against a number of connective tissue macromolecules including elastin, fibronectin, collagen, and proteoglycan. The presence of these enzymes may contribute to the pathology of these diseases.
Normal plasma contains large quantities of protease inhibitors that control a variety of enzymes involved in connective tissue turnover and inflammation. For example, .alpha.-1-antiprotease (.alpha.-1-PI) is a serine protease inhibitor that blocks the activity of both elastase and, at a slower rate, cathepsin G. .alpha.-1-PI has received considerable interest because reduction in plasma levels to less than 15% of normal is associated with the early development of emphysema.
In addition to plasma derived protease inhibitors, secretory fluids, including bronchial, nasal, cervical mucus, and seminal fluid contain an endogenous protease inhibitor called secretory leukoprotease inhibitor (SLPI) that can inactivate both elastase and cathepsin G and is believed to play an important role in maintaining the integrity of the epithelium in the presence of inflammatory cell proteases. In certain pathological states .alpha.-1-PI and SLPI are inactivated by neutrophil oxidative mechanisms allowing the neutrophil proteases to function in an essentially inhibitor-free environment. For example, bronchial lavage fluids from patients with adult respiratory distress syndrome (ARDS) have been found to contain active elastase and .alpha.-1-PI that had been inactivated by oxidation.
In addition to oxidative mechanisms, neutrophils possess non-oxidative mechanisms for eluding inhibition by antiproteases. Neutrophils from patients with chronic granulomatous disease are capable of degrading endothelial cell matrices in the presence of excess .alpha.-1-PI. There is considerable in vitro evidence that stimulated neutrophils can tightly bind to their substrates such that serum antiproteases are effectively excluded from the microenviroment of tight cell-substrate contact. The influx of large numbers of neutrophils to an inflammatory site may result in considerable tissue damage due to the proteolysis that occurs in this region.
Applicants have determined that elastase and cathepsin G are the primary neutrophil proteases responsible for cartilage matrix degradation as measured by the ability of neutrophil lysate, purified elastase and cathepsin G, and stimulated neutrophils to degrade cartilage matrix proteoglycan. Further, applicants have discovered that stimulated neutrophils degrade cartilage matrix in the presence of serum antiproteases indicating that degradation occurs in the serum-protected pericellular area between the neutrophils and substrate. Degradation of cartilage matrix occurring in the pericellular region could be blocked only by inhibiting both elastase and cathepsin G. Applicants have discovered a class of enzyme inhibitors which inhibit both elastase and cathepsin G and are thus useful in preventing neutrophil mediated connective tissue degradation.